1. Field of the Invention
The present invention relates to a novel Raney-type metal porous material and its production method, and further relates to its use as a catalyst.
2. Description of Related Art
Heretofore, based on the characteristic function and activity thereof, Raney-type metals have been investigated for their application to electrode materials, catalysts, etc. For example, regarding electrode materials, there are proposed porous Raney metals of which the surface area has been increased, and those of which the surface including the inner surface of the pores therein has been coated or plated with a different type of metal or alloy to thereby enhance the durability and the activity thereof (Patent References 1 to 3).
Regarding catalysts, for example, it is proposed to prepare a Raney-type Cu—Ni—Zn catalyst by developing a Cu—Ni—Zn alloy with an alkali solution followed by alloying it through hydrogen gas reduction, and to use it as a catalyst for methanol reforming (Patent Reference 4).
However, for Raney-type metals, it is difficult to constitute porous structure-having alloys that have heretofore been investigated; and in fact, no one has heretofore succeeded in developing a practicable method of enhancing the function and the activity of the metals based on the porous structure thereof. Regarding use as catalysts, the relationship between the porous structure that is considered effective in point of increasing the surface area and the catalytic activity thereof is as yet investigated little in the art.
In fact, non-supported porous metal catalysts such as typically Raney-type catalysts have been known through the ages. Of an ordinary supported catalyst, the ingredient that takes actual catalytic activity thereof accounts for only a few percentage of the surface area of the entire catalyst; while on the other hand, a Raney catalyst is efficient in that the entire surface area thereof exhibits catalytic activity. However, almost all conventional Raney catalysts are single metal catalysts, and therefore have a serious problem with thermal stability in that at a high temperature at which the catalytic reaction goes on, the surface area of the catalyst greatly reduces owing to sintering. Regarding supported catalysts, it is possible to produce alloy catalysts of which the composition differs from that of metals, according to an impregnation method or coprecipitation method of using different types of metal salts; however, almost all conventional Raney catalysts are single metal catalysts. Accordingly, Raney catalysts are expected to have only the catalytic function of a single metal alone.
In the known technique for the above-mentioned Cu—Ni—Zn Raney-type catalyst composed of different types of metals, any substantial investigation about the alloy formation and the porous structure is not made. In the case of this catalyst, the three-dimensional alloy of Ni—Cu—Zn is processed for leaching therefore forming a significant concentration fluctuation (inhomogeneousness) of the ingredients, and composition control and porous structure formation for increasing the surface area would be substantially difficult. Therefore, the technique is problematic in that it lacks developability and practicability.    [Patent Reference 1] JP-A 11-111304    [Patent Reference 2] JP-A 58-46553    [Patent Reference 3] JP-A 59-94377    [Patent Reference 4] JP-A 63-256136
In the background as above, the present invention is to make it possible to alloy a Raney-type metal with a porous structure, to realize a novel method of enabling remarkable enhancement of the function and the activity of the alloy based on the porous structure thereof, and to use it for solving the problem with thermal stability of conventional Raney catalysts and for enhancing the catalytic function thereof and adding further diversity thereto.